The present invention relates generally to an electric shaver, and more particularly to an electric shaver of the type having a shear head in which one cutter oscillates with reference to another cutter in response to rotation of the output shaft of the shaver motor.
Electric shavers of this type are known and use a linkage to transmit motion from the motor output shaft to the oscillating cutter. The linkage utilized a crank that is operated by the output shaft of the motor, and a swing arm which is connected with the crank and which effects the oscillatory movement of the oscillating cutter being mounted for swinging or pivoting movement about an axis. In the prior-art constructions, the axis of the motor output shaft, the axis about which the swing arm can pivot and the pivot axis of a joint connecting the crank with the swing arm all extend in parallelism with one another. This prevents tumbling movements of the connected components relative to one another. This arrangement basically operates satisfactorily, but of necessity it requires a considerable amount of space for installation, and is therefore frequently not useable because in many applications space is at a premium.
This is particularly true in the newer generations of electric shavers where the tendency is towards smaller and smaller housing, and in particular to housings which are required to be very flat. An attempt has been made to turn the motor axis through 90.degree. with reference to the construction mentioned above, in order to thus obtain an arrangement which can be installed in a comparatively small housing. This resulted in the central plane of the motor being located in the plane of movement of the components of the linkage, and the joint which connects the swing arm and the crank that form a right angle with one another performs an oscillating movement in a portion of an arcuate path. The crank is required to follow this movement and additionally performs a movement about the longitudinal axis of the swing arm; since the latter is only pivotably mounted on a pivot, the swing arm cannot follow this movement. In order to make this arrangement work, it was necessary in the prior art to utilize a joint having several degrees of freedom, and a universal joint was utilized of the type having two pivots which extend at right angles to one another and are mounted in appropriate supports. This type of component is relatively complicated and the permissible tolerance variations in its manufacture are narrow. Moreover, it requires a relatively large number of operating steps to assemble it. As a result of this, such a universal joint is expensive. The use of expensive components, however, is detrimental in the manufacture of electric shavers which are mass-produced items and whose lose their sales appeal if they are too expensive.
Moreover, such a joint must, of course, be quite small in the context of an electric shaver, and this imposes great difficulties in maintaining the required narrow tolerances; on the other hand, unless the manufacturing tolerances are narrow, it is impossible to avoid undesired noise and vibrations in the use of a dry shaver incorporating such a joint. Again, the manufacturing tolerances must not be too narrow because this would make the joint too stiff and necessitate the use of a stronger electric motor to be able to overcome any resistance in the joint. The use of a stronger motor requires greater weight and larger dimensions for the shaver, and, of course, increases the manufacturing expense. Moreover, especially if the shaver is of the battery-operated type, the use of a larger motor is undesirable because a larger motor requires more electric current and will drain the batteries at an unacceptably high rate.